The effect of early fusion on growth of the spine has been studied in rabbits. Free periosteal grafts from the tibia were transplanted either posteriorly between the spinous and articular processes or postero-laterally between the articular and transverse processes. Sound bony fusion was achieved in both the thoracic and the lumbar spine. Spinal fusion caused local narrowing and wedging of the intervertebral spaces, followed by retardation of growth and wedging of the vertebrae. A progressive structural scoliosis developed after unilateral postero-lateral fusion and a lordosis developed after posterior fusion.